Hydraulic vehicle brake systems are known which are in the form of power brake systems and which, in addition to a master brake cylinder which can be actuated by muscle force and to which wheel brakes are hydraulically connected and which provides the pressure and volume for the actuation of wheel brakes, comprise a further, electrically controllable pressure and volume provision device which actuates the wheel brakes in a “brake-by-wire” operating mode. In the event of failure of the electrically controllable pressure and volume provision device, an actuation of the wheel brakes is performed exclusively by way of the muscle force of the vehicle driver (non-boosted fallback operating mode).
WO 2011/029812 A1, which is incorporated by reference has disclosed an electrohydraulic brake system having a master brake cylinder which can be actuated by way of a brake pedal, having a travel simulator and having a pressure provision device. The wheel brakes are, in a “brake-by-wire” operating mode, charged with pressure by the pressure provision device. In the fallback operating mode, the wheel brakes are charged with the pressure imparted by the driver by way of the master brake cylinder that can be actuated by way of the brake pedal. In the case of the already known brake system, it has proven to be disadvantageous that, in the event of a failure of the actuation means or of the drive of the electrically controllable pressure provision device, large brake pedal travels and/or brake pedal forces have to be imparted by the driver in order to achieve adequate service braking deceleration.
DE 10 2012 205 862 A1, which is incorporated by reference describes a “brake-by-wire” brake system which, in addition to a master brake cylinder that can be actuated by way of a brake pedal, comprises a first and a second pressure provision device. The pressure ports of the second pressure provision device are connected to the input-side ports of the inlet valves of the wheel brakes, such that the inlet valves are arranged between the respective pressure port of the second pressure provision device and the wheel brake. Owing to the throttling action of the inlet valves, the pressure medium flow output by the second pressure source to the wheel brake can be impeded. Furthermore, the boosting module with the second pressure provision device is connected differently to the main module depending on arrangement and design, such that different variants and therefore cumbersome production concepts must be made available.